Power semiconductor devices are widely in use for a large range of power applications, from low voltage chips, computers, locomotives, to high voltage transmission lines. In most circuits, freewheel diodes need to be used in relation with the power semiconductor switching devices such as IGBTs (insulated gate bipolar transistors) or MOSFETs (metal oxide semiconductor field effect transistors) for a continuous load current conduction to avoid large voltage damaging the semiconductor devices and the circuit. High power IGBTs are often supplied as a module with diodes that act as freewheel diodes within the module. IGBTs are typically found in parallel with the diodes. Reliable switching operation of both a power semiconductor switching device and a freewheel diode is of primary importance. Optimisation of the operation is also necessary to obtain high efficiency and low power dissipation of the whole circuit. In order to achieve these aims, one main concern is the current commutation from a freewheel diode to a power semiconductor switching device during the switch-on operation of the main switching device. Excessive diode voltage overshoot and power dissipation associated with the diode reverse recovery resulting from a poor commutation will impose high stresses on both the devices, limiting their application range. In particular, when there is a lack of good control, high power diodes may suffer from punch-through and a resulting snappy recovery with a sudden and large reverse voltage increase accompanied by high-frequency oscillation.
Attempts have been made to control IGBTs and other power semiconductor switching devices by use of feedback control techniques including voltage, dv/dt, current and di/dt feedback control. Open loop networks are also widely employed. However, the freewheel diode cannot be directly controlled. Some lower power circuits even dispense with the diodes and use controlled switching devices in place of them. As a result, while those methods or gate drives embody some of the techniques described above, they fail to properly address the concurrent control of both the power semiconductor switching device and the conventional freewheel diode. They are frequently tailor-made to the application, where the user has to ensure that the commutation results in transient voltages and currents within bounds. Good control is difficult to achieve in many applications as the conditions such as load currents and temperatures are continuously changing. Even using feedback control, the result is highly empirical, and the need to adjust the gate drive for different operating conditions can make conventional methods very undesirable and inefficient.
Background prior art can be found in WO 9743832 and US 2005253165.